touch-devices switch: documentation.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/6381010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@72510 0039d316-1c4b-4281-b951-d872f2087c98

chrome/common/chrome_switches.cc

@@ -1381,6 +1381,9 @@ const char kWebSocketLiveExperimentHost[]   = "websocket-live-experiment-host";
 #endif
 
 #if defined(HAVE_XINPUT2)
+// Tells chrome to interpret events from these devices as touch events. Only
+// available with XInput 2 (i.e. X server 1.8 or above). The id's of the devices
+// can be retrieved from 'xinput list'.
 const char kTouchDevices[]                  = "touch-devices";
 #endif